Because of their typical tough and elastic properties aromatic polycarbonates are employed in numerous industrial fields of use. An occasional disadvantage is the inadequate flame resistance for particularly special requirements, and the low resistance to hydrolysis. These disadvantages have hitherto made it difficult to employ polycarbonates in particularly special requirements in the field of the electrical industry and of domestic equipment. Thus, for example, housing components and instrument components of electrical machinery used at hot water temperatures must not only possess the customary high-impact properties but also high flame resistance and good resistance to hydrolysis (for example in the case of dishwashing machines, egg boilers, and the like).
Flameproof polycarbonates are known. They are prepared, inter alia, by conjoint use of halogen-containing dihydroxy compounds (for example, 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane or 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane) in preparing the polycarbonate. These halogen-containing polycarbonates, above certain halogen concentrations (bromine about 6% by weight, chlorine about 10% by weight) achieve classification V O (previously SE O) in the burning test according to Underwriters' Laboratories Subj. 94.
A disadvantage which manifests itself with these halogen-containing polycarbonates is, that the processing properties (flow characteristics) are markedly poorer than with pure aromatic polycarbonates based on 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A). The mechanical properties also do not reach the level usually associated with polycarbonate. A further disadvantage is the possible formation of hydrogen halide acids in the event of a fire, in which case inestimable consequential damage can arise through corrosion.
It was now the object of the present invention to provide polycarbonate molding materials which are free from halogen or have a low halogen content, which are distinguished by high flame resistance and which do not exhibit the disadvantages described above, such as poor flow and deteriorated mechanical properties.
It has now been found that additions of polyphenylene sulphide to pure aromatic polycarbonates raise the fire resistance of aromatic polycarbonates without loss of the good mechanical properties and of the processing properties. The oxygen index (according to ASTM-D 2863-70) which is a measure of the inflammability in a mixture of oxygen and nitrogen, is also markedly raised through the admixed polyphenylene sulphide. Thus, for example, a test specimen containing 5% by weight of polyphenylene sulphide attains an oxygen index of 0.30 while pure aromatic polycarbonate based on bisphenol A has an oxygen index of 0.24.